Validation of Markerless Motion Capture for Soldier Movement Patterns Assessment Under Varying Body-Borne Loads.

Field performance of modern soldiers is affected by an increase in body-borne load due to technological advancements related to their armour and equipment. In this project, the Theia3D markerless motion capture system was compared to the marker-based gold standard for capturing movement patterns of participants wearing various body-borne loads. The aim was to estimate lower body joint kinematics, gastrocnemius lateralis and medialis muscle activation patterns, and lower body joint reaction forces from the two motion capture systems. Data were collected on 16 participants performing three repetitions of walking and running under four body-borne load conditions by both motion capture systems simultaneously. A complete musculoskeletal analysis was completed in OpenSim. Strong correlations ( r > 0.8 ) and acceptable differences were observed between the kinematics of the marker-based and markerless systems. Timing of muscle activations of the gastrocnemius lateralis and medialis, as estimated through OpenSim from both systems, agreed with the ones measured using electromyography. Joint reaction force results showed a very strong correlation ( r > 0.9 ) between the systems; however, the markerless model estimated greater joint reaction forces when compared the marker-based model due to differences in muscle recruitment strategy. Overall, this research highlights the potential of markerless motion capture to track participants wearing body-borne loads.

The Effects of Torso-Borne Loads on Functional Movement Patterns.

Functional movement patterns are an important aspect of everyday life, and a growing area of interest for determining the risk of injury and performance ability. Police, military, and fire personnel often carry torso-borne loads that increase the demands on the body while performing occupational tasks. The purpose of this study was to compare movement screen results in both a loaded and unloaded condition to identify potential effects that torso-borne body armor load carriage may have on tactical performance. This provided objective data on the effects that external loads may have on functional movement patterns. Twenty-four physically active participants (11 males, 13 females) volunteered and completed the Fusionetics™ Movement Efficiency Test (FMET) in two conditions: loaded (wearing a 13.5 kg tactical vest) and unloaded, in a counterbalanced order. Participants were video recorded performing these movements and scored later. The overall scores, on a scale of 0 to 100, showed a large, statistically significant decline in functional movement pattern quality from the unloaded to the loaded condition (12.6±7.3 points, p<.001, d=1.8). In the subscales, statistically significant declines (p<.001) were seen in the 2-leg squat (d=0.8), push-ups (d=1.1), shoulder movements (d=2.1), and trunk movements (d=0.9). There was no significant effect of load on the cervical movements or 1-leg squat. Overall, torso-borne body armor loading decreased functional movement pattern quality, suggesting the potential benefit of performing loaded movement screens on tactical athletes.

Carrying Police Load Increases Gait Asymmetry in Ground Reaction Forces and Plantar Pressures Beneath Different Foot Regions in a Large Sample of Police Recruits.

BACKGROUND: Although carrying external load has negative effects on gait biomechanics, little evidence has been provided regarding its impact on body asymmetry. The main purpose of the present study was to examine, whether standardized equipment produced greater gait asymmetries in ground reaction force and plantar pressure. METHODS: For the purpose of this study, we recruited 845 police recruits (609 men and 236 women; 72.1% men and 27.9% women) measured in two conditions: (i) 'no load' and (ii) 'a 3.5 kg load'. Absolute values in ground reaction forces and plantar pressures beneath the different foot regions were assessed with pedobarographic platform (Zebris FDM). Asymmetry was calculated as (xright - xleft)/0.5 × (xright + xleft) × 100%, where 'x' represented a given parameter being calculated and a value closer to 0 denoted greater symmetry. RESULTS: Significant differences in ground reaction forces and plantar pressures between the left and right foot were observed, when adding 'a 3.5 kg load'. Compared to the 'no load' condition, carrying 'a 3.5 kg load' significantly increased gait asymmetries for maximal ground reaction forces beneath the forefoot (ES = 0.29), midfoot (ES = 0.20) and hindfoot (ES = 0.19) regions of the foot. For maximal plantar pressures, only the asymmetry beneath the midfoot region of the foot significantly increased (ES = 0.19). CONCLUSIONS: Findings of this study indicate that 'a 3.5 kg load' significantly increases ground reaction force and plantar pressure gait asymmetries beneath the forefoot and midfoot regions, compared to 'no load' condition. Due to higher loads, increases in kinetic gait asymmetries may have negative effects on future pain and discomfort in the foot area, possibly causing stress fractures and deviated gait biomechanics in police recruits.

The effects of shoulder morphology on the distribution of shoulder pressure during load carriage.

To enhance the prevention of shoulder pressure injuries in various load-bearing populations, the effects of shoulder morphology on pressure distribution were investigated. In this study, 69 participants underwent three-dimensional scanning, and based on shoulder morphological characteristic indicators, they were classified into four shoulder types. From these, 28 participants were selected to have the pressure within shoulder regions measured using a pressure-sensing vest while carrying a backpack load equivalent to 15% of their body weight. The results indicated that variations in shoulder morphology significantly impact pressure distribution. The greater bumpiness of the shoulder surface contributed to pressure concentration at specific points, resulting in uneven pressure distribution. The enhanced fullness of the shoulder surface promoted even pressure dispersal across the area. This study provided a theoretical basis for developing more effective shoulder injury prevention and management strategies tailored to load-bearing populations with different shoulder types.

Understanding how different shoulder morphologies affect pressure distribution is crucial for identifying and managing injury risks among various populations. This research highlights those differences in shoulder morphology, such as increased surface bumpiness, lead to pressure concentration at specific points, whereas enhanced surface fullness aids in even pressure dispersal.

Load increases IMU signal attenuation per step but reduces IMU signal attenuation per kilometre.

BACKGROUND: Despite deleterious biomechanics associated with injury, particularly as it pertains to load carriage, there is limited research on the association between physical demands and variables captured with wearable sensors. While inertial measurement units (IMUs) can be used as surrogate measures of ground reaction force (GRF) variables, it is unclear if these data are sensitive to military-specific task demands. RESEARCH QUESTION: Can wearable sensors characterise physical load and demands placed on individuals in different load, speed and grade conditions? METHODS: Data were collected on 20 individuals who were self-reportedly free from current injury, recreationally active, and capable of donning 23 kg in the form of a weighted vest. Each participant walked and ran on flat, uphill (+6 %) and downhill (-6 %) without and with load (23 kg). Data were collected synchronously from optical motion capture (OMC) and IMUs placed on the distal limb and the pelvis. Data from an 8-second window was used to generate a participant-based mean of OMC and IMU variables of interest. Repeated Measures ANOVA was used to measure main and interaction effects of load, speed, and grade. Simple linear regression was used to elucidate a relationship between OMC measures and estimated metabolic cost (EMC) to IMU measures. RESULTS: Load reduces foot and pelvic accelerations (p<0.001) but elevate signal attenuation per step (p=0.044). Conversely, attenuation per kilometre is lowered with the addition of load (p=0.017). Uphill had the lowest attenuation per step (p=0.003) and kilometre (p≤0.033) in walking, while downhill had the greatest attenuation per step (p≤0.002) and per kilometre (p≤0.004). Attenuation measures are inconsistently moderately related to limb negative work (R≤0.57). EMC is moderately positively related to unloaded running (R≥0.39), and moderately negatively related to walking with and without load (R≤-0.52). SIGNIFICANCE: While load reduces peak accelerations at both the pelvis and foot. However, it may increase demand on the lower extremity to attenuate the signal between the two sensors with each step, while attenuation over time reduces with load.

Sex- and age-related differences in kinetics and tibial accelerations during military-relevant movement tasks in U.S. Army trainees.

Lower extremity injuries are prevalent in military trainees, especially in female and older trainees. Modifiable factors that lead to higher injury risk in these subgroups are not clear. The purpose of this study was to identify whether external loading variables during military-relevant tasks differ by age and sex in U.S. Army trainees. Data was collected on 915 trainees in the first week of Basic Combat Training. Participants performed running and ruck marching (walking with 18.1 kg pack) on a treadmill, as well as double-/single-leg drop landings. Variables included: vertical force loading rates, vertical stiffness, first peak vertical forces, peak vertical and resultant tibial accelerations. Comparisons were made between sexes and age groups (young, ≤19 years; middle, 20-24 years; older, ≥25 years). Significant main effects of sex were found, with females showing higher vertical loading rates during ruck marching, and peak tibial accelerations during running and ruck marching (p ≤ 0.03). Males showed higher vertical stiffness during running and peak vertical tibial accelerations during drop landings (p < 0.01). A main effect of age was found for vertical loading rates during running (p = 0.03), however no significant pairwise differences were found between age groups. These findings suggest that higher external loading may contribute to higher overall injury rates in female trainees. Further, higher stiffness during running may contribute to specific injuries, such as Achilles Tendinopathy, that are more prevalent in males. The lack of differences between age groups suggests that other factors contribute more to higher injury rates in older trainees.

The Agreement between Wearable Sensors and Force Plates for the Analysis of Stride Time Variability.

The variability and regularity of stride time may help identify individuals at a greater risk of injury during military load carriage. Wearable sensors could provide a cost-effective, portable solution for recording these measures, but establishing their validity is necessary. This study aimed to determine the agreement of several measures of stride time variability across five wearable sensors (Opal APDM, Vicon Blue Trident, Axivity, Plantiga, Xsens DOT) and force plates during military load carriage. Nineteen Australian Army trainee soldiers (age: 24.8 ± 5.3 years, height: 1.77 ± 0.09 m, body mass: 79.5 ± 15.2 kg, service: 1.7 ± 1.7 years) completed three 12-min walking trials on an instrumented treadmill at 5.5 km/h, carrying 23 kg of an external load. Simultaneously, 512 stride time intervals were identified from treadmill-embedded force plates and each sensor where linear (standard deviation and coefficient of variation) and non-linear (detrended fluctuation analysis and sample entropy) measures were obtained. Sensor and force plate agreement was evaluated using Pearson's r and intraclass correlation coefficients. All sensors had at least moderate agreement (ICC > 0.5) and a strong positive correlation (r > 0.5). These results suggest wearable devices could be employed to quantify linear and non-linear measures of stride time variability during military load carriage.

Effectiveness of a passive military exoskeleton in off-loading weight during static and dynamic load carriage: A randomised cross-over study.

BACKGROUND: Load carriage imposes high physical stresses on the human body, increasing the risk of injuries. This study assessed the effectiveness of a passive military exoskeleton in off-loading the weight placed on the body during heavy load carriage under static standing and dynamic walking conditions. METHODS: Eight full-time regular personnel of the Singapore Armed Forces enrolled in the study. Static loading tests included nine trials of 10-s quiet standing while carrying different loads (0-55 kg) with and without the exoskeleton. For dynamic loading, participants walked on a treadmill on flat, inclined, and declined surfaces while carrying two different loads (25 kg, 35 kg) with and without the exoskeleton. In-shoe normal ground reaction forces (GRF) were recorded during quiet standing and treadmill walking. Differences in total force with and without the exoskeleton during static loading were compared using Wilcoxon one-sample signed ranked tests against zero (no weight off-load) as a reference. Statistical parametric mapping test was used to compare the walking in-shoe GRF-time series with and without exoskeleton use for each load and surface condition. RESULTS: Exoskeleton use was effective in off-loading loads of 2.3-13.5 kg during static quiet standing but the response varied substantially across loads and among the participants. Statistical analysis revealed no meaningful differences in the walking in-shoe GRF with and without exoskeleton use. The results were largely consistent across flat, inclined, and declined surfaces, and both 25-kg and 35-kg loads. CONCLUSIONS: The passive military exoskeleton was effective in off-loading some load from the human body during static quiet standing but not dynamic walking on flat and sloped surfaces. The varied response across loads and participants calls for better design and fitting of the military exoskeleton to individual users.

Short-term effects of running exercise on pinch strength, grip strength, and manual dexterity of the dominant and non-dominant hands.

Occupations including first responders and military require manual tasks; therefore changes in hand strength and dexterity could affect performance. We hypothesised that pinch strength, grip strength, and dexterity will change after unloaded and loaded exercise. Twenty-four male (25 ± 4.0 yrs; 86.3 ± 9.3 kg) and 10 female (25 ± 6.0 yrs; 62.1 ± 5.9 kg) participants completed 3 conditions for 5 minutes: (1) no exercise (2) run with no load at 3.0 m/s and (3) run wearing a 9.1 kg belt. Heart rate was different among conditions (p ≤ 0.05). Pinch strength was significantly different for the non-dominant hand after exercise (p = 0.005) for male participants, but not for the dominant hand. Grip strength was significantly different for the non-dominant hand between loaded and unloaded run (p = 0.035) for male participants. Pinch and grip strength did not change after exercise for female participants. Dexterity times were not different after exercise, but female participants were significantly faster (p ≤ 0.039) than male participants.

Grip strength, pinch strength, and dexterity are maintained in the first 15 minutes after running exercise for male and female participants. The dominant hand should be used if greater and more consistent strength and dexterity are needed for tasks that involve use of the hands after exercise.Abbreviations: ANOVA: Analysis of Variance; CV: Coefficient of Variation; Dom: Dominant hand; Non-Dom: Non-dominant hand.

Coupled effect of load weights and belt use on male shoulder pressure redistribution.

Shoulder pressure redistribution is jointly affected by backpack loads and belt support. However, the combined effect of both factors has rarely been fully evaluated. Here, we studied the coupled effect of backpack loads and belt support on shoulder pressure redistribution. All twenty-eight healthy male subjects underwent eight loading conditions with both chest and hip belts fastened (CH) and unfastened (CON) in four conditions where the backpack weighed 7.5, 15, 22.5, and 30% of body weight (BW). Shoulder pressure distribution was quantified through a pressure-sensing vest mat. The results showed that using the hip belt and chest belt was effective in relieving the high pressure in the lateral clavicle and medial trapezius region and strengthening the load-bearing capacity of shoulder. However, the assistance in pressure relief of using belt was weakened when load increased to 30% BW. This study also showed that the belt use can be effective in improving pressure asymmetry on both sides.

Compression caused by loads may result in shoulder injuries. An in-depth analysis of shoulder pressure distribution is necessary. This study showed that the hip-belt and chest-belt use was effective in relieving the high pressure in the lateral clavicle region and medial trapezius region and strengthening the load-bearing capacity of shoulder.

Influences of backpack loading on recovery from anterior and posterior losses of balance: An exploratory investigation.

Backpacks are common devices for carrying external posterior loads. However, relatively little is known about how these external loads affect the ability to recover from balance loss. In this exploratory investigation, 16 young adults (8 female, 8 male) performed forward and backward lean-and-release balance recovery trials, while wearing a backpack that was unloaded or loaded (at 15% of individual body weight). We quantified the effects of backpack loading on balance recovery in terms of maximum recoverable lean angles, center-of-mass kinematics, and temporal-spatial stepping characteristics. Mean values of maximum lean angles were 20° and 9° in response to forward and backward perturbations, respectively. These angles significantly decreased when wearing the additional load for only backward losses of balance. During backward losses of balance, the additional load decreased peak center-of-mass velocity and increased acceleration by ∼10 and 18% respectively, which was accompanied by ∼5% faster stepping responses and steps that were ∼9% longer, 11% higher, and had an ∼10% earlier onset. Thus, wearing a backpack decreases backward balance recovery ability and changes backward recovery stepping characteristics.

Concentric and eccentric hip musculotendon work depends on backpack loads and walking slopes.

Hip muscle weakness is associated with low back and leg injuries. In addition, hiking with heavy loads is linked to high incidence of overuse injuries. Walking with heavy loads on slopes alters hip biomechanics compared to unloaded walking, but individual muscle mechanical work in these challenging conditions is unknown. Using movement simulations, we quantified hip muscle concentric and eccentric work during walking on 0° and ±10° slopes with, and without 40% bodyweight added loads, and with and without a hip belt. For gluteus maximus, psoas, iliacus, gluteus medius, and biceps femoris long head, both concentric and eccentric work were greatest during uphill walking. For rectus femoris and semimembranosus, concentric work was greatest during uphill and eccentric work was greatest during downhill walking. Loaded walking had greater concentric and eccentric work from rectus femoris, biceps femoris long head, and gluteus maximus. Psoas concentric work was greatest while carrying loads regardless of hip belt usage, but eccentric work was only greater than unloaded walking when using a hip belt. Loaded and uphill walking had high concentric work from gluteus maximus, and high eccentric work from gluteus medius and biceps femoris long head. Carrying heavy loads uphill may lead to excessive hip muscle fatigue and heightened injury risk. Effects of the greater eccentric work from hip flexors when wearing a hip belt on lumbar spine forces and pelvic stability should be investigated. Military and other occupational groups who carry heavy backpacks with hip belts should maintain eccentric strength of hip flexors and hamstrings.

Exploring the physiological benefits of carrying a suspended backpack versus a traditional backpack.

This study investigates the differences in metabolic energy cost and physiological adaptations between carrying a suspended backpack and a traditional backpack during exercise. For that, 30 males completed the Bruce test while carrying a loaded backpack. Researchers used a metabolic system to obtain variables, analysed muscle oxygen saturation, and used a 2-way RM ANOVA. As results, a significant fatigue interaction was found, but the interaction between fatigue and backpack was non-significant. Using a suspended backpack resulted in energetic advantages in oxygen consumption, muscle oxygen saturation, and performance compared to a traditional backpack. In conclusion, this study offers insights into the physiological implications of using a suspended backpack, suggesting it may reduce the risk of musculoskeletal issues and improve performance for those carrying heavy loads.Practitioner summary: The suspended-load backpacks have been proposed as an alternative to traditional backpacks. This study highlighted that the use of a suspended backpack provided some energetical advantages adaptation compared to the traditional backpack in terms of oxygen consumption, muscle oxygen saturation and performance during a multistage treadmill test walking-running test.

Commingling Effects of Anterior Load and Walking Surface on Dynamic Gait Stability in Young Adults.

Treadmill walking has been used as a surrogate for overground walking to examine how load carriage affects gait. The validity of using treadmill walking to investigate load carriage's effects on stability has not been established. Thirty young adults were randomized into 3 front-loaded groups (group 1: 0%, 2: 10%, or 3: 20% of bodyweight). Participants carried their load during overground and treadmill walking. Dynamic gait stability (primary outcome) was determined for 2 gait events (touchdown and liftoff). Secondary variables included step length, gait speed, and trunk angle. Groups 1 and 2 demonstrated similar stability between walking surfaces. Group 3 was less stable during treadmill walking than overground (P ≤ .005). Besides trunk angle, all secondary outcomes were similar between groups (P > .272) but different between surfaces (P ≤ .001). The trunk angle at both events showed significant group- and surface-related differences (P ≤ .046). Results suggested that walking with an anterior load of up to 10% bodyweight causes comparable stability between surfaces. A 20% bodyweight front load could render participants less stable on the treadmill than overground. This indicates that anteriorly loaded treadmill walking may not be interchangeable with overground walking concerning stability for anterior loads of 20% bodyweight.

The Combined Influence of Infant Carrying Method and Motherhood on Gait Mechanics.

Postpartum mothers are susceptible to lumbopelvic pain which may be exacerbated by loading, like carrying their infant in arms and with baby carriers. Nulliparous women carrying infant mannequins may biomechanically mimic mother-infant dyad, but this has not been studied. The purpose of our study was to investigate biomechanical differences of 10 mothers carrying their infants and 10 nulliparous women carrying infant mannequins under 3 gait conditions: carrying nothing, carrying in arms, and carrying in a baby carrier (babywearing). Spatiotemporal gait parameters, peak ground reaction forces and impulses, and lower extremity and trunk kinematics were collected using motion capture and force plates and compared using a mixed 2 × 3 (parity × condition) analysis of variance (α ≤ .05). The largest differences occurred between carrying conditions: carrying in arms or babywearing increased vertical and anteroposterior ground reaction forces, trunk extension, ankle dorsiflexion, and hip and knee flexion. Kinematic differences were identified between arms and babywearing conditions. Together this suggests alterations in joint loading for both groups. Our study also contributes a novel understanding of postpartum health by demonstrating alterations in step time, anterior forces, and ankle and knee mechanics, suggesting that during gait, mothers carrying their own infants choose different propulsive strategies than nulliparous women carrying mannequins.

Head-torso coordination in police officers wearing loaded tactical vests during running.

BACKGROUND: The influence of load carriage in operational police officers is not well understood despite a relatively high injury rate. Assessing load related changes in head and torso coordination may provide valuable insight into plausible injury mechanisms. RESEARCH QUESTION: Do typical police tactical vest loads alter head and torso coordination during running? METHODS: Thirty-eight UK police officers ran at a self-selected pace (>2 ms-1) on a non-motorised treadmill in four vest load conditions (unloaded, and low, high and evenly distributed loads). Peak head and torso tilt, and peak vest displacement were compared between all four conditions. Timings between vest and torso change of direction were compared between the three loaded conditions. The coupling angle between the head and torso calculated using modified vector coding were compared between unloaded and each loaded conditions using Statistical Parametric Mapping. RESULTS: No significant differences were found between conditions for peak head or torso tilt alone (p > 0.05). Loading equipment low on the vest led to significantly greater mediolateral vest displacements (38 mm) away from the torso than a high (34 mm) or evenly distributed (30 mm) conditions. The vest was found to change direction vertically before the torso in the anterior-posterior direction, and then influence torso motion. The loaded conditions changed the head-torso coupling from in-phase (with head-dominancy) to anti-phase (with torso dominancy) between 55% and 77% stance. Anti-phase with a relatively stationary head and the torso rotating forward likely places a greater concentric demand on the posterior neck muscles relative to unloaded running. SIGNIFICANCE: Current tactical vest designs allow significant extra displacement of load away from the body during running, altering coordination at the head and torso.

Differences in running biomechanics between young, healthy men and women carrying external loads.

During U.S. Army basic combat training (BCT), women are more prone to lower-extremity musculoskeletal injuries, including stress fracture (SF) of the tibia, with injury rates two to four times higher than those in men. There is evidence to suggest that the different injury rates are, in part, due to sex-specific differences in running biomechanics, including lower-extremity joint kinematics and kinetics, which are not fully understood, particularly when running with external load. To address this knowledge gap, we collected computed tomography images and motion-capture data from 41 young, healthy adults (20 women and 21 men) running on an instrumented treadmill at 3.0 m/s with loads of 0.0 kg, 11.3 kg, or 22.7 kg. Using individualized computational models, we quantified the running biomechanics and estimated tibial SF risk over 10 weeks of BCT, for each load condition. Across all load conditions, compared to men, women had a significantly smaller flexion angle at the trunk (16.9%-24.6%) but larger flexion angles at the ankle (14.0%-14.7%). Under load-carriage conditions, women had a larger flexion angle at the hip (17.7%-23.5%). In addition, women had a significantly smaller hip extension moment (11.8%-20.0%) and ankle plantarflexion moment (10.2%-14.3%), but larger joint reaction forces (JRFs) at the hip (16.1%-22.0%), knee (9.1%-14.2%), and ankle (8.2%-12.9%). Consequently, we found that women had a greater increase in tibial strain and SF risk than men as load increases, indicating higher susceptibility to injuries. When load carriage increased from 0.0 kg to 22.7 kg, SF risk increased by about 250% in women but only 133% in men. These results provide quantitative evidence to support the Army's new training and testing doctrine, as it shifts to a more personalized approach that shall account for sex and individual differences.

The Influence of Multiple Pregnancies on Gait Asymmetry: A Case Study.

Gait asymmetry is a predictor of fall risk and may contribute to increased falls during pregnancy. Previous work indicates that pregnant women experience asymmetric joint laxity and pelvic tilt during standing and asymmetric joint moments and angles during walking. How these changes translate to other measures of gait asymmetry remains unclear. Thus, the purpose of this case study was to determine the relationships between pregnancy progression, subsequent pregnancies, and gait asymmetry. Walking data were collected from an individual during 2 consecutive pregnancies during the second and third trimesters and 6 months postpartum of her first pregnancy and the first, second, and third trimesters and 6 months postpartum of her second pregnancy. Existing asymmetries in step length, anterior-posterior (AP) impulses, AP peak ground reaction forces, lateral impulses, and joint work systematically increased as her pregnancy progressed. These changes in asymmetry may be attributed to pelvic asymmetry, leading to asymmetric hip flexor and extensor length, or due to asymmetric plantar flexor strength, as suggested by her ankle work asymmetry. Relative to her first pregnancy, she had greater asymmetry in step length, step width, braking AP impulse, propulsive AP impulse, and peak braking AP ground reaction force during her second pregnancy, which may have resulted from increased joint laxity.

Effect of increased running speed and weight carriage on peak and cumulative tibial loading.

INTRODUCTION: Tibial stress injuries are a burdensome injury among military recruits. Military activities include running and the carriage of additional weight, and this may be related to the high risk of bone stress injuries. The aim of this study was to quantify tibial loading when running at two different speeds, with and without additional weight, and to quantify their combined influence. METHODS: Fourteen male distance runners who ran at least 40 km per week ran barefoot on a force-instrumented treadmill in four conditions representing preferred running speed (mean (SD) 3.1 (0.3) m/s) and 20% increased running speed (3.8 (0.4) m/s), with and without 20% of body weight carried in a weight vest. Kinematics and kinetics were synchronously collected. Bending moments were estimated about the medial-lateral axis of the tibial centroid located 1/3rd of the length from distal to proximal. Static equilibrium was ensured at each 1% of stance. Peak bending moments were obtained in addition to cumulative-weighted loading, where weighted loading accounted for the relative importance of the magnitude of the bending moment and the quantity of loading using a bone-dependent weighting factor. RESULTS: There were no interaction effects for running speed and weight carriage on peak or cumulative tibial loading. Running at a 20% faster speed increased peak and cumulative loading per kilometer by 8.0% (p < 0.001) and 4.8% (p < 0.001), respectively. Carriage of an additional 20% of body weight increased peak and cumulative loading per kilometer by 6.6% (p < 0.001) and 8.5% (p < 0.001), respectively. INTERPRETATION: Increasing the physical demand of running by increasing speed or weight carriage increased peak tibial loading and cumulative tibial loading per kilometer, and this may increase the risk of tibial stress injury. Running speed and weight carriage independently influenced tibial loading.

Validation of In-Shoe Force Sensors during Loaded Walking in Military Personnel.

The loadsol® wireless in-shoe force sensors can be useful for in-field measurements. However, its accuracy is unknown in the military context, whereby soldiers have to carry heavy loads and walk in military boots. The purpose of this study was to establish the validity of the loadsol® sensors in military personnel during loaded walking on flat, inclined and declined surfaces. Full-time Singapore Armed Forces (SAF) personnel (n = 8) walked on an instrumented treadmill on flat, 10° inclined, and 10° declined gradients while carrying heavy loads (25 kg and 35 kg). Normal ground reaction forces (GRF), perpendicular to the contact surface, were simultaneously measured using both the loadsol® sensors inserted in the military boots and the Bertec instrumented treadmill as the gold standard. A total of eight variables of interest were compared between loadsol® and treadmill, including four kinetic (impact peak force, active peak force, impulse, loading rate) and four spatiotemporal (stance time, stride time, cadence, step length) variables. Validity was assessed using Bland-Altman plots and 95% Limits of Agreement (LoA). Bias was calculated as the mean difference between the values obtained from loadsol® and the instrumented treadmill. Results showed similar force-time profiles between loadsol® sensors and the instrumented treadmill. The bias of most variables was generally low, with a narrow range of LoA. The high accuracy and good agreement with standard laboratory equipment suggest that the loadsol® system is a valid tool for measuring normal GRF during walking in military boots under heavy load carriage.